Water Chapter 2 p. 47-49

Chemistry Review Bonds Electronegative atoms atoms with a strong attraction for electrons….greedy! Bonds Covalent Sharing of electrons Strong Equal sharing=non-polar covalent Unequal sharing=polar covalent Ionic Attraction between tw0 charge atoms or molecules Positive= CATION Negative= Anion Charges cancel=neutral ionic compound Dissociates in water

Intermolecular forces Hydrogen bonds (not a “true” bond) Between the hydrogen atom in one molecule and an electronegative atom in another molecule (O, F, N) Van der waals forces Attraction between two polar molecules (opposites attract)

Water in Biological systems Biochemical 80% of a living organism composed of water ¾ of Earth covered in water Humans are about 60% water 2 reasons why water is important Major component of cells (70-95% of mass of cell) Provides environment for aquatic organisms to live

Structure of Water Molecule h2O two hydrogen atoms COVALENTLY Bonded to one greedy oxygen Oxygen is electronegative Unequal sharing of hydrogen’s electrons (electrons spend more time around oxygen's orbitals)=Polarity Hydrogens in water molecule have a slightly + charge Oxygen in water molecule has a slightly – charge Dipole small charges on different atoms within a single molecule; unequal distribution of a charge Water has 3 dipoles…2 positive and 1 negative

Hydrogen Bonding & water Hydrogen bonds restrict movement of liquid water Liquid water Constantly forming and breaking hydrogen bonds dense Solid water Hydrogen bonds become fixed (stuck) Less dense than liquid Water’s polarityHydrogen Bonding unique properties of water Solvent properties Thermal properties

Thing to Know: Role of Water in Living Organisms in reference to….. Solvent Action Specific Heat Capacity Latent Heat of Vaporization

Solvent Properties of Water Dipoles on water molecules enable molecules to surround other polar or ionic compounds i.e. sodium chloride in water Polar molecules and ions can dissolve Good solvent This allows water to transport substances around body of organisms Examples: Mammals  blood plasma is mostly water carrying glucose, oxygen, and ions (Na+) Lymphatic, digestive, and excretory systems Plants  nutrients from soil to all parts of the plant Vascular tissue Enables water to be a medium for metabolic reactions Cytoplasm of cells Matrix of mitochondria Stroma of chloroplast

Water as a solvent in plants

Thermal Properties of Water Is liquid at normal earth temperatures H-bonds prevent water molecules from flying away from each other (like a gas) Between 0* and 100* water is liquid Forming and breaking h-bonds constantly Transitory bonds Hydrogen sulfide (h2s) similar structure to water but gas at room temp. b/c it lacks hydrogen bonds

Thermal Properties of Water High specific heat capacity Specific heat Capacity= amount of heat energy that must be added to a given mass to raise the temperature of a substance by 1* C Large amount of energy required to raise temperature of water Small amount needed to heat air Large bodies of water  slow to change temperature as environment changes Stable habitats Inside of organisms primarily composed of water  stable environment stable body temperature Temperature = kinetic energy High temp = high kinetic energy In order to increase temperature of eater, heat must not only increase the kinetic energy of the water molecules, but also break hydrogen bonds

Thermal Properties of Water high latent heat of Vapourisation DEF: a measure of the heat energy needed to vaporize a liquid (cause it to evaporate) Liquid to gas Liquid water to water vapour Because of hydrogen bond, large amounts of energy are needed for vaporization to occur (H-bonds must be broken for water to escape as a gas) Water has high latent heat of vaporization This leads to High heat capacity During vapourization: Energy is transferred to water molecules as they become a gas This means that liquid water remaining loses energy from its surroundings = cooling down of liquid water When water evaporates, it absorbs LOTS of energy form surroundings Evaporation of water has a cooling effect Sweat Panting

Thermal Properties of Water high latent heat of Vapourisation Freezing of water is the opposite of vaporization When going from liquid water to solid ice, water molecules must lose a large amount of energy Water molecules literally release energy when they freeze….this warms up their surroundings… Water underneath a layer of ice warms up, preventing a lake from freezing straight through

Thermal Properties of Water Freezes from the top down Liquid water becomes dense as it cools Water molecules lose kinetic energy and move closer together At 4*c, water is liquid At 0*c, water is solid Water molecules for a lattice Widely spaced water molecules b/c hydrogen bonds are fixed Ice is less dense then water (it floats) Layer of ice = insulator Slows down the loss of heat from the water beneath it Marine organism survive winter Changes in density of water  currents Maintain circulation of nutrients in bodies of water

Cohesive and adhesive properties Adhesion Water sticks to other molecules Walls of xylem Cohesion Water sticks to water High cohesion = high surface tension Capillary Action= adhesion +cohesion

Water as a Reagent A reactant in chemical reactions Examples? Photosynthesis Energy from sun is used to separate the hydrogen ions from the oxygen in the water molecule PHOTOLYSIS sunlight breaking up water molecules into Hydrogen ions and oxygen molecule Hydrogen ions used to fuel the rest of photosynthesis reactions to make glucose (electrons also released to go down ETC) Oxygen molecules are released into the atmosphere as a waste product but used as a reactant in aerobic respiration Hydrolysis reactions Hydro= water Lysis= to break down Water is used to break down larger molecules (like polysaccharides, proteins, fats) Common in digestion

Water Molecule Activity Your group needs to create at least 15 water molecules White = hydrogen Red = oxygen Black Pipe cleaners = covalent bond Colored yarn shows hydrogen bonds Use dry erase boards to label each stage Stages of Water to represent: Liquid water Solid Water Water Vapor A lake covered with a layer of ice Go To table with your assigned number Smart Phone App required: FLIPAGRAM Materials White paper Red paper Black pipe cleaners Colored yarn Scissors dry erase board and marker Smart phone Beige paper (backdrop)

Practice Test Questions Write out question and determine correct answer 11.